1. Field of the Invention
The present invention relates to a method of forming a copper thin film on a substrate by using an organometallic complex as a raw material and a system therefor.
2. Description of the Related Art
A chemical vapor deposition method and a chemical vapor deposition system using an organometallic complex as a raw material has been known as a chemical vapor deposition system for forming a film of a wiring material on a substrate. Copper is thought to be a promising material for forming a wiring material after aluminum, and a thin copper film has been formed by using a chemical vapor deposition method and a system for the chemical vapor deposition method, in which copper hexafluoroacetylacetone (trimethylvinylsilyl) (I) hereinafter expressed by Cu(hfac)(tmvs) in the present specification) is used as a raw material.
In this conventional copper thin film forming method, in order to improve the deposition rate, the adhesion performance and the stability of copper with respect to the surface of a substrate, a method of adding water, water vapor, hexafluoroacetone dihydrate (Hhfac.2H2O) or the like to Cu(hfac)(tmvs), which is a raw material, has been proposed (for example, Chemical vapor deposition of Copper from Cu+1 precursors in the presence of water vapor, Appl. Phys. Lett. 63(20), pp. 2842-2844, and Japanese unexamined patent-publication No. JP-A-10-140352).
In the copper thin film forming method conventionally proposed, in which water vapor or the like is added to a raw material gas, the water vapor is added during the formation of a thin film. However, this method presents drawbacks of producing micro-voids and increasing the concentration of impurities (fluorine: F, oxygen: O, carbon: C) in the formed copper thin film.
For this reason, there has been room for developing a method and system for forming a copper thin film having an excellent adhesion performance and the same level of specific resistance as bulk, and which is capable of undergoing mass production as a method for forming the wiring of a semiconductor system.
It is the object of the present invention to provide a method and a system for forming a copper thin film by chemical vapor deposition in which the adhesion performance of a copper thin film to a substrate is improved, and in which a copper thin film having a low concentration of impurities and an excellent specific resistance is formed.
In order to accomplish the object described above, the copper thin film forming method proposed by the present invention is a method of forming a copper thin film, in which a raw material gas is introduced into a substrate processing chamber storing a substrate and which is under a reduced pressure so as to form a copper thin film on the substrate. In particular, the method includes introducing an addition gas in addition to the raw material gas at the initial stage of deposition. Thereafter, the introduction of the addition gas is stopped, while the introduction of raw material gas is continued.
The above-described copper thin film forming method is adopted in a seed process for forming a thin film of, for example, from about 20 nm to 100 nm in thickness on a diffused barrier film or an adhesion layer film made of TiN, Ta, TaN, TiSiN, TaSiN, and the like.
In the case of a buying process for forming a thin film of about 500 nm to 2000 nm, it is possible to adopt another copper thin film forming method of the present invention. In particular, at the initial stage of deposition, an addition gas is introduced in addition to the introduction of the raw material gas. Thereafter, the introduction of the addition gas is stopped, whereas the introduction of the raw material gas is continued, and the introduction of the addition gas is conducted at predetermined intervals of time, whereby the copper thin film is formed.
In the above-described copper thin film forming methods of the present invention, the introduction of the addition gas conducted at the initial stage of deposition in addition to the introduction of the raw material gas is intended to produce an excellent adhesion performance. The introduction of the addition gas is required to be conducted at least for the minimum time of about 0.5 seconds so as to accomplish this object.
On the other hand, a long introduction time for the addition gas increases the number of micro-voids generated, which is not preferable, and the continuous introduction of the addition gas during the deposition process increases the concentration of impurities and the number of micro-voids generated, which is also undesirable. Therefore, it is desirable that the introduction time for the addition gas is about 30 seconds at the longest, depending on the length of time of deposition.
In the above description, in the case of the burying process for forming a thin film of about 500 nm to 2000 nm, at the initial stage of deposition, an addition gas is introduced in addition to the introduction of the raw material gas. Thereafter, only the introduction of the raw material gas is continued to so as form a film, and the introduction of the addition gas is repeatedly conducted at predetermined intervals of time. This process is conducted in order to reduce the concentration of impurities in the copper thin film and continue forming the dense film, to prevent a decrease in deposition rate, and further to prevent the surface of the copper thin film from becoming rough.
Therefore, it is desirable that after the introduction of the addition gas is completed at the initial stage of deposition, the introduction of the addition gas is conducted at intervals of time in accordance with the time when the deposition rate decreases or the time when the surface of the copper thin film being formed becomes rough. As described above, since the introduction of the addition gas at this time is intended to recover the decreased deposition rate or to prevent the surface of the copper thin film being formed from becoming rough, at least about 0.5 seconds is good enough for the length of time for the introduction of the addition gas.
In any of the copper thin film forming methods described above in accordance with the present invention, the following steps can be performed. First, the introduction of the addition gas into the substrate processing chamber is conducted. Thereafter, while continuing the introduction of the addition gas, the introduction of the raw material gas into the substrate processing chamber is started to start depositing, and the introduction of the addition gas is continued during the initial stage of the deposition process.
It is known that the separation of the copper thin film, which indicates a decrease in adhesion performance, develops at the interface between the copper thin film and a diffused barrier film. Therefore, an effective method for improving the quality of the interface (in particular, an adhesion performance) is to introduce the addition gas into the substrate processing chamber before the introduction of the raw material gas into the substrate processing chamber is started so as to start depositing. Thus, the surface of the substrate on which the diffused barrier film is formed as an underlying film is exposed to the atmosphere of the addition gas.
In the above description, the addition gas may be any one of a water gas (that is, steam made by evaporating water) a gas made by evaporating an alcohol derivative such as methyl alcohol, ethyl alcohol, and isopropyl alcohol; a gas made by evaporating a carboxylic acid derivative such as acetic acid and pyromellic acid; and a gas made by evaporating a xcex2-diketone derivative such as acethylacetone, hexafluoroacetylacetone, and dihydroxymethane. It is possible to form a copper thin film having good adhesion performance and an excellent film quality by the above-described methods in accordance with the present invention using any one of them.
In this respect, if the water, the alcohol derivative, the carboxylic acid derivative, and the xcex2-diketone derivative are subjected to a process for removing dissolved oxygen therein and are evaporated, and then the gas is added, it is possible to form a copper thin film having a further excellent film quality.
Further, the introduction of the addition gas into the substrate processing chamber may be conducted by introducing a water gas (that is, steam made by evaporating water filled into a gas cylinder, which is connected to the substrate processing chamber) into the substrate processing chamber from the gas cylinder.
The gas cylinder can be connected to the substrate processing chamber by and through any 1 of the following mechanisms. For example, the gas cylinder may be connected to the substrate processing chamber with a flow control mechanism therebetween. Alternatively, the gas cylinder may be connected to a carrier gas introducing pipe with a flow control mechanism therebetween. Furthermore, the carrier gas introducing pipe may be connected to a vaporizer in a raw material gas introducing mechanism for supplying a raw material gas to the substrate processing chamber. The steam made by evaporating water can be introduced into the substrate processing chamber from the gas cylinder by any 1 of the above-described mechanisms.
If an addition gas which is a water gas (that is, steam made by evaporating water) is introduced into a substrate processing chamber from a gas cylinder filled with the steam, the concentration of water with respect to a carrier gas (for example, argon gas) can be correctly adjusted in advance. Accordingly, it is possible to supply the steam to the substrate processing chamber stably and correctly. Since water is liquid at a normal temperature and a normal pressure, the pressure of water can not be increased to a pressure more than a saturated vapor pressure when the water is filled into a gas cylinder. Therefore, the above-mentioned carrier gas (for example, argon gas) is necessary, and the use of the carrier gas makes it possible to fill steam into the gas cylinder under a high pressure of, for example, 150 kg/cm2 to the extent of about 300 ppm by volume.
Next, a system for forming a copper thin film proposed by the present invention so as to accomplish the object described above comprises: a substrate processing chamber the inside of which can be held under a reduced pressure; a substrate supporting mechanism for supporting a substrate in tie substrate processing chamber, a substrate temperature control mechanism for keeping the substrate at a predetermined temperature; and a raw material gas introducing mechanism for evaporating a liquid raw material or a solid raw material into a raw material gas and for supplying the raw material gas to the substrate processing chamber in. An addition gas introducing mechanism includes a mechanism for removing dissolved oxygen in a liquid addition material and a mechanism for evaporating the liquid addition material, from which dissolved oxygen is removed, and is connected to the substrate processing chamber via a flow control mechanism.
As described above, in the system for forming a copper thin film as proposed by the present invention, the flow control mechanism is disposed between the substrate processing chamber and the addition gas introducing mechanism. Therefore, the addition gas can be introduced into the substrate processing chamber only at initial stage of the deposition process or at an initial stage of the deposition process and at predetermined intervals of time during the following deposition, further before the start of the deposition process.
Further, as described above, the addition gas introducing mechanism includes the mechanism for removing dissolved oxygen in the liquid addition material and the mechanism for evaporating the liquid addition material from which the dissolved oxygen is removed. Therefore, the addition material from which the dissolved oxygen is previously removed is evaporated and introduced into the substrate processing chamber, whereby the quality of copper thin film formed on the substrate can be improved.
In this regard, in place of the addition gas introducing mechanism including the mechanism for removing dissolved oxygen in the liquid addition material and the mechanism for evaporating the liquid addition material from which the dissolved oxygen is removed, a gas cylinder may be adopted which is filled with steam made by evaporating water.
In this case, the gas cylinder can be connected to the substrate processing chamber by and through any 1 of the following mechanisms. For example, the gas cylinder can be connected to the substrate processing chamber with a flow control mechanism therebetween. Alternatively, the gas cylinder can be connected to a carrier gas introducing pipe with a flow control mechanism therebetween. The carrier gas introducing pipe can also be connected to a vaporizer in a raw material gas introducing mechanism for supplying a raw material gas to the substrate processing chamber.
If the gas cylinder filled with steam made by evaporating water is adopted, as described above, it is possible to simplify the configuration of the addition gas introducing mechanism and to supply a necessary concentration of steam to the substrate processing chamber stably and correctly using a simple operation.
According to the present invention, in a method and a system for forming a copper thin film by the chemical vapor deposition (CVD) method using an organometallic complex, it is possible to improve the adhesion performance of a copper thin film to a substrate and to form a copper thin film of high purity and excellent quality, which has a small amount of impurities (such as F, O, C) in the formed copper thin film, few micro-voids, and which has the same level of specific resistance (1.7 xcexcxcexa9cm) as bulk.